DE3918136A1 - METHOD FOR PRODUCING MANAGE-CONTAINING PHOSPHATE COATINGS ON METAL SURFACES - Google Patents

Description

The present invention relates to a method for producing manganese-containing phosphate coatings on surfaces made of steel, galvanized Steel, aluminum and / or their alloys by spraying or diving.

To improve corrosion protection and paint adhesion Consumer goods such as automobile bodies, automotive accessories and spare parts, agricultural equipment, refrigerators and any Type of small parts phosphated according to the so-called low-zinc process and then mostly cataphoretically dip-coated. Such Manganese modified zinc phosphate coatings as a primer for modern painting systems are for example from W.A. Roland and K.-H. Gottwald, metal surface, 1988/6 known. Here it is determined that the use of manganese ions in addition to zinc and Proven to be nickel ions in low-zinc phosphating processes Corrosion protection improved, especially when used surface-coated sheet. The incorporation of manganese in the Zinc phosphate coatings lead to smaller and more compact crystals with higher alkali stability. At the same time, the working width increased by phosphating baths; aluminum can also be combined with Steel and galvanized steel are phosphatized, whereby the generally achieved quality standard is guaranteed. Such composite parts, which are made from a wide variety of materials, For example, aluminum and steel are used in automotive engineering used more and more recently.  

EP-A 02 61 704 describes a process for producing phosphate coatings known on such surfaces, whereby by Spraying or splash-dipping to form even phosphate layers with a high degree of coverage with a phosphating solution in addition to zinc and phosphate, there is at least one accelerator as well as an exact amount of fluoride ions must have. Furthermore, according to EP-A 02 61 704, the content of free acid (FS) according to a formula mentioned there.

In contrast, the object of the present invention is an improved one Process for the production of phosphate coatings on surfaces made of steel, galvanized steel, aluminum and / or their alloys to provide that to even more uniform phosphate coatings leads, with a change of Phosphating technology should not be required.

The above object has been achieved by a process for producing manganese-containing phosphate coatings on surfaces made of steel, galvanized steel, aluminum and / or their alloys or aluminum-steel composites by spraying or spray-dipping with an aqueous solution
0.8 to 1.4 g / l Zn ²⁺ ,
0.6 to 2.0 g / l Mn ²⁺ ,
0.3 to 1.4 g / l Ni ²⁺ ,
10 to 25 g / l PO₄ ^3- ,
2 to 10 g / l NO₃⁻,
0.2 to 1.0 g / l F⁻ and
as an accelerator of phosphate separation
0.04 to 0.12 g / l NO₂⁻,
0.6 to 2.0 g / l ClO₃⁻ and / or
0.2 to 1.0 g / l of sodium 3-nitrobenzenesulfonate, the free acid content being adjusted to 1.4 to 1.8 points and having a total acid content of 18 to 30.

As is known, the content in conventional low-zinc processes is of free acid about 0.6 to 0.9 points. With beyond increased values are formed on the metal surfaces treated in this way uneven, not closed phosphate layers; on Steel is also observed to form rust film. By the addition of manganese is used in the fluoride-containing phosphating baths in principle an increase in the free acid content without the mentioned Disadvantages possible.

The use of manganese in the phosphate layer has been found in the above mentioned substrate surfaces various advantages.

With the help of the present invention it has been found that in particular when using the method according to the invention on aluminum surfaces a relatively small amount of fluoride is used can be used to achieve optically uniform phosphate layers.

Surface treatment of steel can lead to the formation of Phosphophyllite or manganese-containing phosphophyllite the proven Low zinc technology can be maintained while maintaining the Zinc content can be increased without loss of quality.

On galvanized, alloy-galvanized steel sheets and on aluminum leads to the use of manganese while increasing the zinc content due to the manganese incorporation in the layer in the subsequent Coating by means of cataphoretic electrocoating improved results. This simultaneous interaction of the  Levels of zinc and manganese were in the phosphating solution Surprisingly found with the help of the present invention.

The aluminum materials to be treated by the method according to the invention include the pure metal and its alloys. As Examples are therefore pure aluminum, AlMg and AlMgSi kneading materials called. A detailed description of these materials is the aluminum paperback, 14th edition, aluminum publishing house, Düsseldorf, 1983. With the help of Steels to be treated according to the method of the invention are in particular Consumer goods such as automobile bodies, automobile accessories and -spare parts, agricultural equipment, refrigerators and others Types of small parts that are usually used in the form of sheets Find. The term "galvanized steel" includes galvanizing by electrolytic deposition and hot-dip application and thus refers to zinc and known zinc alloys.

When carrying out the method according to the invention in spray-immersion mode the spraying time must be designed such that a largely closed phosphate layer is formed.

Modern full immersion systems are characterized by a large number consecutive steps. The term "full immersion system" results from the phosphating by dipping application. At other process steps, spraying operations are also carried out, being after the body emerged from the immersion bath is injected. It is important for optimal phosphating a separate activation step. For pre-cleaning and activation The layer to be phosphated is usually divided into several Operations cleaned, rinsed and then before the Phosphating activated. For example, titanium phosphate can be used here aqueous suspensions are used.  

Compliance with the concentration ranges according to the main claim is an essential component for the production of qualitative high quality, d. H. uniform phosphate coatings. At If the concentrations are undershot, the layers become uneven. In particular, their suitability for later Electro dip painting.

The fluoride concentrations mentioned according to the invention are included a special ion-sensitive electrode in a buffered solution measured at pH 5.3. Therefore these values are in no way comparable with the values mentioned in the prior art, in which the concentration of fluoride directly in the phosphating solution was measured.

In a preferred embodiment of the present invention, the process is characterized by the use of an aqueous solution containing 0.8 to 1.0 g / l Zn ²⁺ ,
0.8 to 1.2 g / l Mn ²⁺ ,
0.3 to 0.8 g / l Ni ²⁺ ,
14 to 20 g / l PO₄ ^3- ,
3 to 6 g / l NO₃⁻ and
0.3 to 0.6 g / l F⁻.

The surfaces coated using the above method can then in known processes for the Electrocoating can be used. Accordingly, there is one Another embodiment of the present invention in use the procedure for preparing the surfaces for the Electro dip painting.

The invention is illustrated by the following examples.

example 1

Within the usual process sequence with the stages:
Cleaning, rinsing, (activating) phosphating, rinsing, re-passivation, VE rinsing, the conversion treatment was carried out under the following bath conditions in accordance with the three compositions A, B and C:

• - For steel, phosphophyllite or manganese-containing phosphophyllite is the "low zinc" technology maintained and the zinc content increased without loss of quality will.
• - On galvanized, alloy-galvanized steel sheets and on aluminum takes place through the manganese incorporation in the layer in the following Coating with a KET primer is a clear one Improvement of the corrosion protection results (see example 2).

The determination of the mass per unit area after application of the process variant A on the individual substrates according to DIN 50 942 following measured values (mean values):

Steel St 1405 2.0 g / m²
Steel, electrolytically galvanized 2.4 g / m²
Aluminum (AlMg 0.4 Si 1.2) 2.8 g / m²
Aluminum (AlMg 4.5 Mn) 2.7 g / m²

The manganese content of the was determined by atomic absorption spectrometry (AAS) Phosphate layer determined quantitatively (mean values):

Steel St 1405 6.4%
Steel, electrolytically galvanized 4.7%
Aluminum (AlMg 0.4 Si 1.2) 6.2%

X-ray diffraction shows the manganese-containing phosphate layers no new specific gang found.  

With the help of the VDA alternating climate test (VDA test specification 621 415) the corrosion resistance of the following Phosphating coatings with different substrates were examined. Following the coating, a standard electrophoresis dip paint was used (KET primer FT 85 7042 from BASF Farben und Lacke) used.

The test time of the VDA alternating climate test is 5 to 10 rounds. During this time, the treated substrate is made according to the DIN 50 017 KFW exposed to an alternating condensation water climate. Farther the substrate is determined within the test period Time at room temperature (18 to 28 ° C) according to DIN 50 014 stored. Furthermore, as part of this alternating climate test Salt spray test according to DIN 50 021 carried out.

After the test cycles were completed, the following data were determined.

A Phosphating solution, containing manganese

B phosphating solution, manganese-free (comparison)

Claims (4)

1. A method for producing manganese-containing phosphate coatings on surfaces made of steel, galvanized steel, aluminum and / or their alloys or aluminum-steel composites by spraying or spray-dipping with an aqueous solution containing
0.8 to 1.4 g / l Zn ²⁺ ,
0.6 to 2.0 g / l Mn ²⁺ ,
0.3 to 1.4 g / l Ni ²⁺ ,
10 to 25 g / l PO₄ ^3- ,
2 to 10 g / l NO₃⁻,
0.2 to 1.0 g / l F⁻ and
as an accelerator of phosphate separation
0.04 to 0.12 g / l NO₂⁻,
0.6 to 2.0 g / l ClO₃⁻ and / or
0.2 to 1.0 g / l of sodium 3-nitrobenzenesulfonate, the free acid content being adjusted to 1.4 to 1.8 points and the solution having a total acid content of 18 to 30. 2. The method according to claim, characterized in that one containing an aqueous solution
0.8 to 1.0 g / l Zn ²⁺ ,
0.8 to 1.2 g / l Mn ²⁺ ,
0.3 to 0.8 g / l Ni ²⁺ ,
14 to 20 g / l PO₄ ^3- ,
3 to 20 g / l PO₄ ^3- ,
3 to 6 g / l NO₃⁻ and
0.3 to 0.6 g / l F
starts. 3. Process according to claims 1 to 2, characterized in that which produces phosphate coatings on aluminum-steel composites will. 4. Application of the method according to claims 1 to 3 for preparation of surfaces for electrocoating.